Lasers have been extensively utilized for excising pathological, exterior tissues, such as skin, and have been suggested for excising interior pathological tissues, by utilizing invasive techniques. The pathological tissue is excised in response to the laser producing high intensity electromagnetic fields that vaporize and damage the tissue lattice. The laser damage field coincides with the electromagnetic, optical field so that the size or volume of excised tissue can be very accurately controlled. The laser beam creates holes or cuts in the tissue by disrupting bonds in the chemical network of tissue. The problems involved in invasive, rather than noninvasive, laser surgery are well known and have been dealt with, to a certain extent, by others. For example, invasive laser systems, or laser systems which appear to be adaptable to invasive applications, are disclosed in the following United States Patents:
______________________________________ Snitzer 3,471,215 Bredemeir 3,659,613 Ayres 3,467,098 Bredemeir 3,710,798 Bredemeir 3,804,095 Sharan 3,865,114 Wallace et al. 3,906,953 ______________________________________
A particular problem involved in invasive laser surgery is propagating the beam to the pathological tissue to be excised without damaging intermediate tissue between the pathological tissue and an opening in the body cavity through which the beam must enter. High intensity, coherent, optical radiation derived from the laser has a tendency to heat guiding structures through which it propagates. If the guiding structure contacts the intermediate tissue, there is a tendency for the intermediate tissue to be excessively heated and possibly burned to a serious extent. An instrument that contacts the intermediate tissue must be chemically inert with the tissue so that it does not cause any infection, thermal burns or other deleterious effects on that tissue. In addition, it is desirable for the cross sectional, circular area of the irradiating beam to be small in certain instances and larger in other instances. It is also frequently desirable to excise the pathological tissue so that the cross section of the excised tissue, in a plane at right angles to the exterior surface of the tissue, is frusto-conical, with the largest face of the frusto-conical section being below the surface to reduce blood flow from the tissue and promote faster healing of the treated area of the organ.
It is accordingly, an object of the present invention to provide a new and improved apparatus for and method of excising pathological tissue with a laser beam.
A further object of the invention is to provide a new and improved instrument for and method of excising pathological tissue from the interior of a living animal with a laser beam that is introduced into the body cavity without causing any substantial adverse effects on tissue within the body cavity between the entrance to the body cavity and the pathological tissue.
A further object of the invention is to provide a laser instrument for and method of excising pathological tissue wherein laser energy is coupled to the pathological tissue without substantially heating intermediate tissue between an opening in the body cavity and the site of the pathological tissue.
An additional object of the invention is to provide a laser instrument for excising pathological tissue within the body cavity wherein energy from the laser source irradiates the pathological tissue with an optical wave guiding cannula that is chemically inert with intermediate tissue between the opening to the body cavity and the pathological tissue.
Still another object of the invention is to provide a new and improved apparatus for and method of excising pathological tissue from the interior of a living organism by forming relatively small diameter, substantially frusto-conical cross sectioned excised regions in the tissue, wherein the conical cross section increases as a function of depth from the surface to the tissue.